Quantum fluid reveals hidden states that can be switched with a magnetic field

Bose-Einstein condensates (BECs) are often described as a "fifth state of matter": a quantum state in which many particles lose their individual identities and behave as one collective object. For more than 60 years, researchers have sought to create such condensates from excitons-electron-hole pairs-as a solid-state route to macroscopic quantum coherence, which is useful for quantum technologies. This has been difficult to realize in controllable semiconductor devices because optically ...